Continuous rotation potentiometer



p 2, 9 8 L. Hikbwfly' 5 2,850,604" I CONTINUOUS ROTATION POTENTIOMETER Filed Feb; 8, 1957 DISPZACfNE/Vf 0F OUTPUT SHAFT 40 INVENTOR Lor/M/R h. Eek LEV ATTORNEY United States Patent CONTINUOUS ROTATION POTENTIOMETER Lothair H. Rowley, Syosset, N. Y., assignor to Sperry Rand Corporation, Ford Instrument Company Division, Long Island City, N. Y., a corporation of Delaware Application February 8, 1957, Serial No. 639,098

4 Claims. (Cl. 201-48) This invention relates to potentiometers as used in electrical and electronic circuits and in particular to improvements in single turn potentiometers having a shaft driven sliding contact which can be angularly displaced beyond 360 in either direction.

As is presently known, a single turn potentiometer has a stator resistor which is disposed along a circular are having a fixed radius, the circular are being slightly less than 360. Normally no restrictions are imposed upon the movement of the slider and the potentiometer shaft is free to rotate beyond 360. In designing a conventional single turn potentiometer for shaft displacements up to and beyond 360, a choice is normally made between either having a small dead space between the beginning and end of the stator resistor which produces a small open output circuit position as the slider approaches the 360 position, or allowing the sliding contact to short circuit the stator resistor over a small incremental displacement of the potentiometer shaft.

A principal object of this invention is to provide an improved single turn potentiometer having substantially no output dead space and no input short circuit position for continuous shaft displacements up to and beyond 360.

Another object of this invention is to provide a potentiometer having an improved linear output response relative to input shaft displacements.

As presently contemplated, a potentiometer system comprises a pair of single turn otentiometers, each having open or dead space sectors, connected in parallel branch circuits across a pair of input terminals. Each branch circuit has included therein an impedance element to compensate for the impedance that was omitted when the dead space sector was'established. The potentiometers are ganged with their shafts out of phase and an averaging circuit means is provided to average out errors of non-linearity, the averaging circuit means being normally responsive to both potentiometers and to only one potentiometer output when the other potentiometer output is open circuited over its dead sector interval.

These and other features, capabilities and advantages of the invention will appear from the subjoined detailed description of one embodiment thereof illustrated in the accompanying drawings in which:

Fig. l is a schematic diagram of a continuous linear single turn potentiometer; and

Fig. 2 is a diagram illustrating the principles of operation of the improved potentiometer.

Referring to Fig. 1, a potentiometer circuit has two input terminals 11 and 12, and two output terminals 13 and 14, terminals 12 and 14 being connected to ground. Two branch circuits 15 and 16 are connected across input terminals 11 and 12. Branch circuit 15 includes a fixed resistor 17 in series connection with a stator resistor 18 of a single turn potentiometer 19 having a dead space sector of dA degrees as measured clockwise from the end terminal x to the beginning terminal y of the stator resistor 18, the resistor 17 being connected between terminal 11 and point y of the stator resistor 18.

Branch circuit 16 comprises a fixed resistor 20 in series connection with a stator resistor 21 of a single turn potentiometer 22 having a dead space sector of dB degrees as measured clockwise from the end terminal m to the beginning terminal n of the stator resistor 21, the resistor 20 being connected between end terminal m of the stator resistor 21 and the terminal 12 or ground. A resistor 30 is connected between the sliding contact 31 of potentiometer 19 and the sliding contact 32 of potentiometer 22 by conductors 33 and 34, respectively. The resistor 30 has a tap 35 which is connected to the output terminal 13 by a conductor 36.

The resistor 17 has a discrete resistive value corresponding to the product of the dead space sector dA expressed in degrees and the angular rate of resistance change along the stator resistor 18, viz.,

R dA Woo-(1A and for the branch circuit 16,

The shafts of potentiometers 19 and 22 are ganged so that sliders 31 .and 32 are equally displaced by an angular displacement of a common output shaft 40 connected thereto. However, the sliders 31 and 32 are phase displaced by an angle equal to dA degrees, the slider 32 being advanced in a clockwise direction relative to the slider 31. Hence, when the slider 31 is displaced 0 from position x by a like displacement of the output shaft 40', the slider 42 will be positioned at (6+dA) degrees.

In Fig. 2 is shown a diagram of the variation of the voltage across output terminals 13 and 14 for various displacements of the output shaft 40 when a reference voltage V is impressed upon input terminals 11 and 12 from a source not shown. On the assumption that potentiometers 19 and 22 are linear, the segment OF of the characteristic is covered by potentiometer 19 and the segment EG is covered by the potentiometer 22, the dead space dA being represented by the segment PG and the dead space dB being represented by the segment OE. If the characteristics of the otentiometers 19 and 22 are not identical in regard to linearity, the segment EF will be a function of the individual characteristics of the potentiometers as a result of the averaging effect of the tapped resistor 30.

As output shaft 40 and slider 31 approach the x position, which is both the 0 and 360 reference point, slider 32 will approach the point 11. With selective adjustments, slider 32 will contact point It at a very small incremental displacement after slider 31 passes point 2:. With such a fine adjustment, the width of the zero voltage or open position can be very narrow without short circuiting the output circuit. In the event that slider 32 contacts point n at the same time that slider 31 contacts point x, the entire input voltage is absorbed by the resistance of resistor 30 and the output voltage across terminals 13 and 14 is momentarily equal to V/ 2 as represented by point H in Fig. 2 if the tap 35 on resistor 30 is at the center. When either slider 31 or 32 is in a dead space sector, the output from the other slider is conducted to the output terminal 13 through one-half of resistor 30. However, the added resistance of one-half the resistance value of resistor 30 does not introduce any error in the output response when the potentiometer is driving a high impedance load. As an alternative adjustment the tap 35 on resistor 30 may be removed to either end. In this case point H does not exist and the voltage drops immediately from point G to zero. I

From the foregoing, it will be seen that the characteristics of a standard commercial type of single turn potentiometer is improved by the addition of a second similar standard commercial potentiometer with associated circuitry such as had been disclosed herein.

It is to be understood that various modifications in the circuitry other than those above described may be effected without departing from the principle and scope of the invention as defined in the appended claims.

What is claimed is:

1. A potentiometer circuit means by which a substantially uninterrupted output is obtained from a single turn continuous rotation potentiometer, said circuit comprising a voltage source, a first potentiometer and a second potentiometer similar to said first potentiometer connected in parallel to one terminal of said voltage source; said first and second otentiometers each having an annularly disposed resistance element of slightly less than 360 thereby providing a dead space sector between the ends thereof, and a radially disposed rotatably mounted contact arm, said second potentiometer contact arm being angularly displaced from said first potentiometer contact arm in a clockwise direction by an amount substantially equal to said dead space sector, and means by which said first potentiometer contact arm and said second potentiometer contact arm are rotated in unison in a clockwise direction; conductor means by which the input ends of said first and second potentiometer resistor elements are connected in parallel to said voltage source and by which the other ends of said first and second potentiometer resistance elements are connected to a ground, a first trim resistor interposed in said conductor means in series with said first potentiometer, a second trim resistor interposed in said conductor means in series With said second potentiometer, the impedance of each of said trim resistors being a function of the total resistance of the resistance element and the dead space sector of the associated potentiometer, an electrical connection between the contact arms of said first and second potentiometer, a resistor interposed in said electrical connection and having a tap by which the output of said circuit means is adapted to be connected to a load.

2. A potentiometer circuit means as defined in claim 1 in which said first trim resistor is interposed in said conductor means between the input end of said first potentiometer resistance element and said voltage source and said second trim resistor is interposed in said conductor means between the said other end of said second potentiometer resistance element and said ground.

3. A potentiometer circuit means as defined in claim 2, in which said first trim resistor has a resistance value equal to dA Ra 360-dA and said second trim resistor has resistance value equal to M 360dB wherein the dead space sector of said first potentiometer is dA degrees, the dead space sector of said second potentiometer is dB degrees, the resistance of said first potentiometer resistance element is Ra, the resistance of said second potentiometer resistance element is Rb, and the relative displacement between the potentiometer contact arms is dA degrees.

4. A potentiometer circuit means as defined in claim 1, in which said first trim resistor has a resistance value equal to dA Ra and said second trim resistor has resistance value equal to wherein the dead space sector of said first potentiometer is dA degrees, the dead space sector of said second potentiometer is dB degrees, the resistance of said second potentiometer resistance element is Rb, and the relative displacement between the potentiometer contact arms is dA degrees.

References Cited in the file of this patent UNITED STATES PATENTS 

